The present invention is directed to fire detection apparatus and more particularly to an incipient fire detector employing a particulate monitor.
There are many fire detection systems and devices available, and their operation is based on a wide variety of principles. Most require the presence of flame, fly ash ("smoke"), attainment of a preset temperature level, or the like, and thus that the fire actually exists before it can be detected. It is understood that many of these are complex, subject to contamination, false alarm prone, and/or fail to detect fires under use conditions.
It was felt that a need existed for fire-detection apparatus which could detect a fire in its incipiency, that is, could detect and warn of a hazardous condition that if unattended might lead to a fire, and do this detection with a significant reduction in, and the possibility of complete elimination of, false alarms. This type of detector would have general utility, but would be particularly advantageous for use in isolated areas, aircraft, space vehicles, submarines, and where large concentrations of electronic equipment are present as in computer facilities, to name a few examples. To meet this need, the present invention was devised.
A study was undertaken to find an inherent by-product of an incipient fire condition that could be reliably detected without false alarms. It was found that when combustible materials are heated, some parts may vaporize and recondense in the air as sub-micron particulates thus increasing significantly the concentration of small particulates beyond the distribution normally present. It was subsequently learned that this phenomena of a large flux of sub-micron particles being present during an incipient fire condition had previously been observed by others.
This abnormal increase in sub-micron particulates invariably precedes the onset of combustion. Tests were run during the study on a variety of materials to verify this phenomena. For example, there is a wide variation in the ignition temperature of Coolanol 35 and silicone rubber. In tests of both substances using a gradual increase in temperature, the signals obtained were similar even though the temperatures at which the signals occurred were widely different. As the temperature rose in both cases toward the ignition point, the signal remained steady until pre-pyrolitic decomposition occurred just before ignition. At this time an abnormal sub-micron-particle emission took place and was detected.